#2118: ST_Boundary support for Triangle type

git-svn-id: http://svn.osgeo.org/postgis/trunk@11358 b70326c6-7e19-0410-871a-916f4a2858ee
#2118: add enhanced note to ST_Boundary  (to note Nathan Wagner ST_Triangle support feature)

git-svn-id: http://svn.osgeo.org/postgis/trunk@11359 b70326c6-7e19-0410-871a-916f4a2858ee